1. Field of the Invention
This invention relates to a method for the manufacture of a composite copper-arsenic compound mixture from a nonferrous smelter's or refinery's intermediate byproduct containing copper and arsenic, the composite copper-arsenic compound mixture being useful as an intermediate for the production of a chromium-copper-arsenic type wood antiseptic.
2. Description of the Prior Art
Antisepsis of wood is carried out by either compressively injecting a solution of antiseptic chemicals into wood, by spreading such a solution on wood, by spraying wood with the solution, or by immersing wood in an aqueous solution of the antiseptic agent. Of the noted methods, the most effective and most extensively practiced method is the one which resorts to the compressive injection of the antiseptic solution.
Chemicals which are used in the compressive injection method include creosote, which is an oily substance, and phenol-inorganic fluoride and chromium-copper-arsenic compounds, which are soluble in water. Of these chemicals, the most advantageous is the chromium-copper-arsenic compound. The antiseptic agent prepared from the chromium-copper-arsenic compound not only produces an antiseptic effect but it also exhibits a conspicuous ability to repel ants, and it also displays great adhesiveness to wood. This agent, therefore, will tend not to flow out of the wood to which it is applied and undesirably smear articles placed nearby.
At present, the chromium-copper-arsenic compound type agent (hereinafter referred to briefly as "CCA type agent") is prepared by users (persons engaging in the business of antisepticizing wood) by purchasing the individual chromium, copper and arsenic compounds, and then dissolving them in water according to a prescribed formula.
As the raw materials for the CCA type agent, chromium trioxide or potassium dichromate is used as the source of chromium, cupric oxide or copper sulfate as the source of copper, and arsenic acid or pyroarsenic acid as the source of arsenic. The proportion in which these compounds are combined to form the agent is fixed in Japan by Japanese Industrial Standard K-1554 as shown in Table 1, for example. The dealers engaging in the business of wood antisepsis formulate the CCA agent in accordance with this standard.
TABLE 1 ______________________________________ K.sub.2 Cr.sub.2 O.sub.7 50 .about. 60 weight % No. 1-A CuSO.sub.4.5H.sub.2 O 30 .about. 37 As.sub.2 O.sub.5.2H.sub.2 O 10 .about. 13 CrO.sub.3 59 .about. 67 weight % No. 1-B CuO 16 .about. 20 H.sub.3 AsO.sub.4 17 .about. 21 ______________________________________
When the CCA type agent is prepared in accordance with the formula of No. 1-A, however, the K.sup.+ ions and the SO.sub.4.sup.2- ions inevitably enter as impurities into the agent. Even after the agent has been injected into wood and the chromium, copper, arsenic, etc., have been deposited fast in wood, these ions continue to exist in their water-soluble states. When the antisepticized wood is exposed to rainwater or some other form of water, therefore, these ions are caused to dissolve out of the wood. The escape of these ions is undesirable.
Since these ions act to enhance electric conductivity, the wood which has been antisepticized with the CCA agent described above may allow current leakage when it is used as an electric pole. If SO.sub.4.sup.2- and other an ions are present in a large amount in the agent at the time the agent is applied to wood, the agent causes corrosion in pressurized containers, pumps, pipes and other iron materials. Thus, the materials used in antisepticizing facilities are limited in this respect. Further, there is the possibility of the CCA agent causing corrosion on nails and other metallic articles used in and on the antisepticized wood.
Since the CCA agent of the aforementioned formula No. 1-A suffers from such drawbacks as described above, the CCA agent of the formula No. 1-B, which does not permit inclusion of K.sup.+ and SO.sub.4.sup.2- ions, proves to be more desirable insofar as it does not entail such drawbacks. In the preparation of the CCA agent of the formula No. 1-B, however, cupric oxide is required to be used as the source of copper and it must be dissolved in chromium trioxide and arsenic acid or pyroarsenic acid.
Unfortunately, cupric oxide is not a readily soluble substance. It becomes necessary, therefore, to prepare an aqueous solution containing arsenic acid or pyroarsenic acid in a very high concentration (on the order of 60% by weight of H.sub.3 AsO.sub.4, for example), and to blend stated amounts of chromium trioxide and cupric oxide in the aqueous solution to cause a reaction and produce a highly viscous and aqueous solution as a preparatory step. Since this dissolution entails evolution of heat, it is not easy work.
Moreover, each of the utilized arsenic acid, pyroarsenic acid, cupric oxide or copper sulfate are required to have a fairly high purity, and such high purity materials are expensive; thus the production costs for the CCA agent are high. Use of the formula No. 1-B, therefore, involves many problems.
An object of this invention, therefore, is to provide a method for efficient manufacture of a composite copper-arsenic compound mixture which can be used as an intermediate for producing the CCA type agent which avoids the aforementioned problems encountered by the prior art.